Wasps are parasitizing caterpillars less often under climate change

Changing interactions could lead to a decline in important ecosystem services like pest control

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Caterpillar Costa Rica

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Assessing the impacts of climate change is essential for scientists who want to understand ecosystem dynamics. However, until recently, relatively few studies have linked climate variability to species interactions.

Researchers used data from 22 years of sampling at the La Selva Biological Research Station in Costa Rica to generate statistical models that measure changes in insect species diversity and richness and make future predictions. (Richness is a measurement of how many species are in a given area; diversity takes into account how many species there are as well as the number of individuals of each species.) Researchers looked at two types of insects: caterpillars and parasitoids. Parasitoids are a type of insect whose larvae live as parasites (usually in other insects) that eventually kill their hosts. These types of insects offer an important ecosystem service through species interactions by preventing outbreaks of herbivorous insects (like caterpillars) that can damage wild plant populations or crops in areas of agriculture. 

Forest trees Costa Rica

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The researchers found that species richness and diversity has declined in both caterpillars and parasitoids. Results suggest that these declines are partly driven by climate change and weather anomalies such as extreme precipitation and episodes of warmer than average temperatures, which have been occurring at an increasing rate at La Selva. Alongside the decreases in diversity and species richness, there has been a decrease in the interaction richness between caterpillars and parasitoids. A reduction in parasitism means that there is less biological control over herbivorous caterpillar outbreaks, which decreases ecosystem stability. By extrapolating the data for the next 100 years, this study predicts there will be a 30% drop in parasitism (compared to the 6.6% drop seen over the 22 year study period). These findings support the hypothesis that climate change is contributing to insect species declines. Further research is needed to explore the impacts of declining species interactions.